Intake manifold runners include pipes designed to deliver a flow of air to combustion chambers within an engine. However, during certain parts of the engine drive cycle, intake valves are closed and prevent the air from flowing. When one or more intake valves open, a pressure wave develops within the runner and may increase the amount of air entering the open cylinder chamber. Therefore, under some operating conditions (e.g. at certain RPMs), the time when the propagating pressure wave encroaches upon the intake valve may align with intake valve opening, which causes a significant improvement in the volumetric efficiency and thereby the performance of the engine. For this reason, the airflow may depend on the geometry of a runner. For instance, the time for a pressure wave to propagate through a long manifold runner and back to an intake valve is longer compared to the length of time in a short manifold runner. As such, an engine with longer runners may have a torque peak at a lower RPM range than an engine with short intake runners, which may instead have a power peak at a higher RPM.
In an attempt to accommodate a range of engine conditions, intake manifolds with variable length runners spread out the torque curve into a broad, more manageable profile. Previous variable runner length designs may include continuously variable and discretely variable lengths. Continuously variable intake manifold runners vary the length of a runner with no substantial change to the runner shape or cross-sectional area. Because of the constant cross-sectional area, under some engine conditions, the variable length runner may degrade torque output and thereby decrease fuel efficiency. On the other hand, discretely variable runners typically have preset long and short runner configurations and so often have a pronounced valley of low torque output. An example intake manifold system with continuously variable runners that couple a change in length to a change in cross-sectional area is shown in U.S. Pat. No. 5,687,684 and U.S. Pat. No. 5,762,036. However, the manifold assembly described therein includes parts with intricate groove-like features and non-symmetrical shapes that may be fabricated by a time consuming injection mold process.
The inventor has recognized the disadvantages of the approaches described above and herein discloses a manifold assembly encased in a plenum chamber that includes flexible intake manifold runners coupled to an actuator shaft on one end and to an intake port of an engine on the other end. The flexible manifold runner may be comprised of a helically braided tube. This design allows for a continuously variable runner length, cross-sectional area and tube shape with reduced artificial obstructions to the flow of air to an intake port.
The present description may provide several advantages. In particular, extension of a biaxially braided tube causes a decrease in the cross-sectional area, with the reverse occurring as the tube is compressed. Therefore, an intake manifold runner can be tuned over a wide operating band from low RPM torque to high RPM power in a manner that depends on the operating conditions of the engine. As such, the method allows a cost-effective measure to control the flow of air to the engine based on engine speed and load. Furthermore, because the change of runner length can be calibrated to the change in cross-sectional area, the method may be implemented in various engine systems for optimal engine performance based on the speed and load on the engine, which thereby increases fuel efficiency.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.